* Exit if loading an invalid identity from disk
Previously, if an invalid identity was loaded from disk, ZeroTier would
generate a new identity & chug along and generate a brand new identity
as if nothing happened. When running in containers, this introduces the
possibility for key matter loss; especially when running in containers
where the identity files are mounted in the container read only. In
this case, ZT will continue chugging along with a brand new identity
with no possibility of recovering the private key.
ZeroTier should exit upon loading of invalid identity.public/identity.secret #2056
* add validation test for #2056
ARM Cryptography Extension is optional and not all ARM CPUs support it.
For example, the CPU in Raspberry Pi 4 does not support it.
Check for `__ARM_FEATURE_CRYPTO` before attempting to use the optional
extension.
`__ARM_FEATURE_CRYPTO` is defined by both clang and gcc when the target
has the cryptography extension.
Fixes#1854.
Adam Ierymenko
Joseph Henry
Brenton Bostick
Grant Limberg
Gleb Mazovetskiy
Grant Limberg
staphen